Electron discharge device



Jan. 19, 1943. A. E. ANDERSON 2,308,800

ELECTRON DISCHARGE DEVI-CE Filed Feb. 15, 1941 lNVENTOR :1. E. ANDERSONA T TORNEY mediate vicinity of the axis are Patented Jan. 19, 1943ELECTRON DISCHARGE DEVICE St. George, N. Y., assignor to Bell TelephoneLaboratories, Incorporated, New York, N. Y., a corporation of New YorkApplication February 15, 1941, Serial No. 379,103

Alva Eugene Anderson,

9 Claims.

This invention relates to electron discharge devices and moreparticularly to electrode systems, commonly designated as electron guns,for producing a beam of electrons in such devices.

In general, electron beam discharge devices comprise an electron gun forproducing an electron beam, an electron receiving electrode, such as atarget or anode, upon which the beam is directed, and one or moreauxiliary electrodes between the electron gun and the electron receivingelectrode for affecting or controlling the direction, intensity orvelocity of the beam or withdrawing energy therefrom. The electron gunusually comprises a cathode and two or more electrodes in cooperativerelation therewith for concentrating the electrons emanating therefrominto a beam, one of the electrodes being main tained at a positivepotential with respect to the cathode and commonly referred to as theaccelerating anode.

Two of the factors of considerable import in determining the operatingcharacteristics of such devices and affecting the merit thereof are themagnitude of the current which can be obtained in the beam from acathode'of a particular rating and the degree to and uniformity withwhich the electrons in the beam can be affected or controlled at anyparticular region in the path traversed by the beam. In known devices,usually the attainment of a beam current fairly large in comparison tothe total emission obtainable from the cathode necessitates the use ofrelatively high potentials upon the accelerating anode. Consequently,such devices have a relatively low perveance, the perveance beingexpressed by the relation I being the total beam current and V thevoltage of the accelerating anode.

It has been found also that in electron beam devices wherein theelectrodes are constructed and arranged to constitute an axiallysymmetrical system, the fields extant in the major portion of the pathtraversed by the beam are of considerably less intensity along and inthe vicinity of the axis of the system than at points removed from theaxis. Hence, those electrons in the beam which traverse paths on and inthe imafiected less by potentials on the auxiliary electrodes, orconversely have less effect upon the auxiliary .electrodes, than thosewhich traverse paths .somewhat removed from the axis, whereby .both theefficiency and the frequency range of operation of the device arelimited and non-uniform interchange of energy between the beam and theseelectrodes results.

One general object of this invention is to improve the operatingcharacteristics of electron beam discharge devices.

More specifically objects of this invention are to" beam distion, anelectron gun comprises a cathode having a relatively large area emissivesurface and a plurality of electrode members in cooperative relationwith the cathode emissive surface for concentrating the electronsemanating therefrom into a beam of annular cross-section throughout themajor portion of its length.

In a specific construction, the emissive surface conforms to an annularsection of a toroid and the concentrating system includes inner andouter electrode members extending from the boundaries of the emissivesurface and a pair of coaxial electrodes having juxtaposed portionsdefining an annular passageway converging away from'the emissive surfaceand coaxial therewith.

The invention and the various features thereof will be understoodmoreclearly and fully from the following detailed description with referenceto the accompanying drawing, in which:

Fig. l is an elevational view partly in section of an electron dischargedevice including an'electron gun illustrative of one embodiment of thisinvention, a portion of the electron gun being broken away toshowdetails thereof;

Fig. 2 is an enlarged view in section, along plane 2-2 of Fig. 1 of theelectron gun; and

Fig. 3 is an enlarged outline view showing the configuration andrelation of surfaces of the electrodes in the electron gun illustratedin Fig. 2.

Referring now to'the drawing the electron dis- Attain a high perveancein electron beam disenclosing vessel members 23 and disc 24, it will beapparent, serve charge device shown in Fig. 1 comprises an elongatedevacuated enclosing vessel I0, for example of vitreous material, havingat one end thereof an inwardly extending stem II' from which an anodeI2, of metal or carbon, is supported by rigid leading-in conductors I3.The anode I2 is j generally cup-shaped asshownto minimize secondaryelectron emissive effects. An electron gun, described in detailhereinafter, is mounted adjacent the other end of the enclosing vesselIII,

in coaxial relation with the anode I2 and sup:

ported by leading-in conductors sealed in the end wall of the enclosingvessel I0.

Mounted between the electron gun and the anode I2 are a pair ofcentrally apertured electrodes I4 and I5, coaxial with the electron gun.These electrodes, although shown as discs, may

be of various forms and utilized for various pur 1 poses. Severalformswhich'they: may take and various functions thereof are disclosed inPatent 2,281,717, granted May 5, 1942 to Arthur L. Samuel. Although buta single pair of electrodes has been shown in Fig. 1, it will beunderstood that several pairs or an odd number of electrodes may beprovided depending upon the intended oper- I allel to the flange H, theelectrodes I9 and 23 being insulated from the member I6 by the gaps'therebetween. The electrode I9 is supported by a leading-in conductorsecured to an elongated stem on the electrode I9 extending through thehub I8. The accelerating anode 2i] is supported by rigid conductors 22.aflixed to. the annular portion 2 I and sealed in the end wall of'thevessel II] as shown in Fig. 1.

A plurality of substantially hemispherical metallic members 23 aremounted in spaced relation on the flange H, the outermost member 23being s'ecured,,as by welding, 'to a metallic disc 24 which is supportedfrom leading-in conductors by rigid tie wires or connectors M. Theinnermost member 23 defines a chamber with the dished metallic member I5in which an insulated heater filament 26 is positioned, the ends of theheater filament 26 being 'connectedto leading-in conductors sealed inthe end wall of the III as shown. The metallic as shields to reduce theradiation of heat from the heater filament, so that efficient heating ofthe emissive surface of the member I 6 is realized.

In a particular construction especially advantageous-for use in deviceswherein a magnetic field is employed to focus or otherwise affect theelectron beam, the accelerating anode 20 and the heat shields 23 aremade of magnetic material whereby the member I6 is 'eifectively shieldedfrom the magnetic field.

The configurations and relation of the electrodes of the electron gunare of particular character so that a conical converging electron beamannular in section and focussed at a point on the axis of alignment ofthe several electrodes of the device is produced. In general, theconfigurations and relations are determined in accordance with theprinciples and methoddescribed in Patent 2,268,197, granted December 30,1941 Moreover, it has been established that a high to John R. Pierce, sothat substantially all of the electrons emanating from the emissiveportion of the member I6 traverse rectilinear paths in flowing tothe'focal point of the beam. The specific configurations and relationwill be seen'most clearly from Fig. 3. As shown in thisfigure, thedishedsurface of the. member I6, which is gen-- erally toroidal andsymmetrical about the axis of alignment of the electron gun and theanode V I2, includes an arcuate portion I6a, which is coated with amaterial having good thermionic emission characteristics, and inner andouter non-emissive flanged portions I62) and IE0 respectively, generallyL-shaped in section. The angle 0 of the arcuate portion is substantially126.5 degrees; The electrodes I9 and 20 have juxtaposed frusto-conicalsurfaces I9a and 20a respectively of equal angles defining an annularpassageway converging away from the emissive surface I6a. The angle ,8of the surfaces I9a and 20a is substantially 60 degrees. The surfacesI9a and 20a, it willbe noted project into the gap between thejuxtaposedends of the beam forming elements I 6?) andIGc. a g

During operation of the device, the electrodes I9 and 20 are maintainedat'positive potentials with respectto the member I6. They, may be biasedatthe same potential or the potential "of theelectrode I9 may be greateror less, forexample of the order of 20 per cent than that of H theelectrode to control to some extent the focal point of the'beam;

The portions I61) and I60, same potential as the emissive surface I6a,function as beam forming electrodes and in 'CQODQY', ationwith theaccelerating anodes I9 and 20 concentrate substantially all of theelectrons emanating from the emissive surface I6a into a hollow conicalbeam having a focal point F on the axis of the system and in which all:of the electronstraverse substantially rectilinear paths. The boundariesof the beam are indicated by the dotted lines in Fig. 3.;

There is thus obtained an efiicient electron gun inasmuch as the totalbeam current is commensurate withthe total emission from the surfaceI6a, and also a concentrated sharply focussed beam. Furthermore, it willbe appreciated that substantially uniform fields are realized within;

the beam boundaries, whereby uniform; control of all the electrons inthe beam and uniform transfer of energy therebetween and electrodes,such as the electrodes I4 and I5, is enabled.- In

addition, efiicient operation at frequencies; of. the

order of 3,000 to 30,000 megacycles is possible.

beam current can be obtained with relatively low potentials, for example200 volts, on the accelerating anode 20 so that a perveance of as highas 30 10- isrealized. if

Although in the specific embodiment shown and described the beamformingelectrode members IBb and IE0 are'structurally integral with theemissive portion IBa they may, be physically separate therefrom,for-example spaced from the edges of the emissive portion .I6a of theorderof 10 mils, and electrically connected to the emissive portion.Such construction is especially advantageous if creepage of the emissivecoating to the beam-forming portions isfound to be :suf ficient torender the portions IBb'and IGcemissive and thereby'reduce the sharpnessof the focussing of the electron beam. Also, althoughin the specificconstruction shown and described, the

whiclrare a the eratrices composed of straight lines, they may havecurved generatrices conforming substantially to those shown.Furthermore, it will be understood that various other modifications maybe made in the specific construction shown and described withoutdeparting from the scope and spirit of this invention as defined in theappend-- ed claims.

What is claimed is:

1. An electron gun comprising a cathode having an annular electronemissive surface, and means for concentrating electrons emanating fromsaid surface into a hollow conical beam, said means comprising a pair ofelectrode members extending inwardly from the inner and outer boundariesof said emissive surface and forming an annular gap symmetrical withrespect to and inclined toward the longitudinal axis of said cathode anda pair of spaced electrodes opposite said surface and defining anannular passageway coaxial therewith.

2. An electron gun comprising a cathode having a circular electronemissive surface arcuate in section, a pair of electrode membersextending from the inner and outer boundaries of said emissive surfaceinclined toward one another and defining an annular gap, and a pair ofelectrodes opposite said surface and having juxtaposed surfaces definingan annular passageway coaxial with said gap and converging awaytherefrom.

3. An electron gun comprising a cathode having a dished annular electronemissive surface, a pair of electrode members extending inwardly fromthe boundaries of said emissive surface and defining an annular gap, anda pair of electrodes coaxial with said emissive surface, said electrodeshaving juxtaposed conical surfaces extending into said gap and definingan annular passageway ooaxial with said emissive surface and convergingaway therefrom.

4. An electron gun comprising an electrode having a dished annularsurface the inner and outer edge portions of which are non-emissive andthe intermediate portion of which is coated with an electron emissivematerial, and means including said edge portions for concentratingelectrons emanating from said emissive surface into a hollow electronbeam, said means including also a pair of spaced electrodes oppositesaid annular surface and forming an annular passageway coaxialtherewith.

5. An electron gun comprising a cathode having a dished annular surfacethe intermediate portion of which is arcuate in section and electronemissive and the inner and outer portions of which are non-emissive andinclined toward each other, an annular electrode opposite said outerportion and having a frusto-conical inner surface, and a secondelectrode opposite said inner portion and having an outer frusto-conicalsurface opposite said first frusto-conical surface and definingtherewith an annular passageway converging away from said annularsurface.

6. An electron gun comprising a cathode having a dished annular electronemissive surface inclined toward and symmetrical with respect to thelongitudinal axis of said cathode, and a pair of electrodes oppositesaid surface and coaxial therewith, one of said electrodes being annularand having a frusto-conical inner wall, and the other of said electrodeshaving a frusto-conical portion opposite said frusto-conical wall anddefining therewith an annular passageway converging away from saidemissive surface.

'7. An electron gun comprising a cathode having an annular surfaceconforming to an oblique section of a toroidal surface, a portion ofsaid annular surface being electron emissive, an electrode oppositesaid. annular surface, coaxial therewith and adjacent the inner edgethereof, and a second electrode having an outer portion adjacent theouter edge of said annular surface and having also an annular innerportion encompassing said first electrode and defining therewith anannular passageway coaxial with said annular surface.

8. An electron gun comprising a cathode having an annular substantiallytoroidal surface, an electron emissive coating on the central portion ofsaid surface, an electrode within the boundary of said surface, adjacentthe inner edge thereof and having an outer surface tapering awaytherefrom, and a second electrode having an outer portion adjacent theouter edge of said first surface and an inner frusto-conical wallopposite and of substantially the same form as said tapering outersurface and defining therewith an annular passageway coaxial with saidfirst surface and converging away therefrom.

9. An electron gun comprising a cathode having a dished annular surfacethe edge portions of which extend toward one another, an electronemissive coating on the central portion of said surface, and a pair ofelectrodes in juxtaposition to said surface to concentrate the electronsemanating therefrom into a hollow conical beam converging away from saidsurface, one of said electrodes including an outer portion overlying theouter edge of said surface and an inner frusto-conical wall extendingwithin the boundaries of said surface and coaxial therewith, the largerend of said wall being toward said surface, and the other of saidelectrodes overlying the inner edge of said surface and having afrustoconical wall extending into the space bounded by said first walland tapering in the same direction as said first wall.

ALVA EUGENE ANDERSON.

